How twin studies can inform us about the etiology of addiction.

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Nick Martin
Queensland Institute of Medical Research
Brisbane, Australia

Research has shown that alcohol dependence (AD) and other addictions have a strong genetic component. Although AD has long been recognized as familial, quantification of its heritability was first initiated in large-scale modern twin and family studies which estimate that about two thirds of variance in liability is genetic in origin. Furthermore, evidence is that it is largely the same genes acting in males and females and there are no significant sex differences in etiology by sex. Twin studies have also been performed on component traits such as alcohol metabolism rate, psychomotor sensitivity and alcohol use traits such as age of initiation, normal and maximal consumption, binge drinking and problems with alcohol use. These, and parallel studies on equivalent traits for other substances including nicotine, cannabis, opioids and caffeine as well as addictive gambling will be reviewed, in particular from the point of view of how they have justified the large-scale GWAS studies now being conducted on these substance use and addiction phenotypes.